This application discloses alternatives to and improvements upon the apparatus disclosed in U.S. Pat. Nos.: 3,298,449--Bachman, Moore, Rollins & Garrett 1967; 3,399,738--Haspert; 3,797,589--Kellner & Alther; 3,799,277--Kellner; 4,040,494--Kellner 1977; 4,040,495--Kellner & Garrett 1977; assigned to the same assignee as the present application, the disclosures of which are incorporated herein by reference and the art cited in which may also be referred to for the background of the invention.
The hydraulic thruster has a primary use for applying a force to an earth boring drill bit. A typical application would be to use in directional drilling when the hole angle approaches horizontal. In these situations most of the drill collar or drill stem weight is directed toward the low side of the hole and very little is left for available bit thrust.
This device can make a valuable contribution at this time, because of the high cost of offshore well platforms. It is important for best economics to drill wells a great distance horizontally from each platform to drain as much of the reservoir as possible with a minimum number of platforms. This is known as extended reach drilling. Conventional drilling becomes impractical when the hole wall friction becomes too great and the length of drill stem that must be run in compression for effective bit thrust exceed design limits. There are many other applications where the surface platform must be substantially removed from the hole bottom in the reservoir such as in arctic regions, mountains, and near large cities.